Hydroxyl polymer polymeric structures, such as fibrous elements, produced from crosslinking hydroxyl polymers are known in the art. It is known to crosslink hydroxyl polymers together via a crosslinking agent, such as a dihydroxyethyleneurea (DHEU), in combination with a crosslinking facilitator that prevents unacceptable crosslinking of the hydroxyl polymers by the crosslinking agent to occur. The challenge of managing the crosslinking of the hydroxyl polymers is especially problematic when spinning fibrous elements from an aqueous hydroxyl polymer melt composition.
Ammonium salts, such as ammonium chloride, ammonium sulfate, and ammonium citrate, are known to act as crosslinking facilitators within aqueous hydroxyl polymer melt compositions. Such ammonium salts are initially inactive crosslinking facilitators (catalysts) in the aqueous hydroxyl polymer melt compositions, but become active acid catalysts during heating of an embryonic polymeric structure formed from the aqueous hydroxyl polymer melt composition during a curing step. The problem with such ammonium salts, which are kosmotropic salts, such as ammonium sulfate and/or ammonium citrate, in the aqueous hydroxyl polymer melt composition at the level necessary for complete curing during the curing step, is that they can induce salting out of the hydroxyl polymer, which results in weaker polymeric structures formed therefrom during the polymer processing step.
Another negative that results from the addition of ammonium salts, such as ammonium chloride, ammonium sulfate, and ammonium citrate is increased uptake of water from storage of the polymeric structures under humid conditions. This results in a change in the tensile properties of the polymeric structures depending on atmospheric environment which is undesirable for consumer products, such as sanitary tissue products, employing the polymeric structures.
In addition to the negatives discussed above, the presence of ammonium sulfate in the aqueous hydroxyl polymer melt compositions lowers the Critical Micelle Concentration (CMC) of any fast wetting surfactants, such as sodium sulfosuccinate diester salts, present in the aqueous hydroxyl polymer melt compositions, which in turn decreases the fast wetting surfactants' wetting ability. This decreased wetting ability limits the fast wetting surfactants' ability to increase drying of the polymeric structures formed from the aqueous hydroxyl polymer melt compositions. This ultimately results in negatives in the fibrous elements, for example in increased diameters of fibrous elements formed from the aqueous hydroxyl polymer melt composition.
In addition, carboxylic ammonium salts, such as ammonium citrate, undesirably buffer the pre-cured polymeric structure's pH to above pH 5, which prevents complete crosslinking of the hydroxyl polymers to occur during the curing step.
Finally other salts, such as ammonium chloride, tend to also impart an undesirable yellow color to the polymeric structure during the high temperature of the curing step. Additionally, ammonium chloride causes corrosion of the processing equipment used to make the polymeric structure.
In light of the above, currently used crosslinking facilitators do not facilitate sufficient crosslinking of the hydroxyl polymers present in an aqueous hydroxyl polymer melt composition during the production of the polymeric structures to provide the polymeric structures with acceptable physical properties, such as strength, and color properties.
Formulators of non-aqueous polymer compositions such as non-aqueous polymer coating compositions useful is automobile repair finishing have utilized ammonium sulfosuccinate diester salts as an acid catalyst to activate amino resin crosslinking agents to produce a non-aqueous film coating. However, nowhere do the formulators of such non-aqueous polymer coating compositions teach or suggest using such ammonium sulfosuccinate diester salts in aqueous hydroxyl polymer melt compositions, especially for producing fibrous elements, such as filaments, from such aqueous hydroxyl polymer melt compositions.
Another problem is faced in cases where the fibrous elements are produced from aqueous polymer compositions, for example aqueous hydroxyl polymer melt compositions comprising hydroxyl polymers, such as polysaccharides. Hot drying air is used to remove water from the aqueous hydroxyl polymer melt compositions during spinning in order to produce the fibrous elements, which may be collected to form a fibrous structure. Removal of water from the incipient fibrous elements aids in inhibiting the fibrous elements from sticking to one another during the spinning and/or collecting processes. Failure to effectively remove water from the fibrous elements during formation results in relatively poor tensile properties, such as relatively lower fail stretch (FS), relatively lower total dry tensile (TDT), and/or relatively lower total energy absorbed (TEA), in the fibrous structures produced from the ineffectively dried fibrous elements. It is believed that these poor tensile properties in the fibrous structure are caused, at least in part, by excessive bonding of fibrous elements to one another that occurs when the fibrous elements are not effectively dried. However, the use of larger amounts of drying air is economically infeasible and energy intensive. In addition, ineffectively dried fibrous elements exhibit relatively larger average diameters, which impact various properties of the fibrous structures produced therefrom.
In the past, formulators have combined a crosslinking agent, such as DHEU, simple salts, such as ammonium chloride (NH4Cl), and a fast wetting surfactant, such as a sodium sulfosuccinate diester salt, in an aqueous hydroxyl polymer melt composition to produce filaments. It has been unexpectedly found that the filaments spun from such an aqueous hydroxyl polymer melt composition and/or web formed from the filaments exhibit a salt level as represented by their Conductivity as measured according to the Conductivity Test Method described herein that is higher than desired (i.e., greater than 130 microsiemens) for consumer products, for example sanitary tissue products.
Accordingly, one problem faced by formulators of hydroxyl polymer polymeric structures from aqueous hydroxyl polymer melt compositions is the reduction of the level of salts (i.e., non-sulfosuccinate diester salts), such as ammonium chloride and/or sodium chloride and/or other simple salts, that have in the past been believed to be necessary for facilitating crosslinking via a crosslinking agent present in the hydroxyl polymer polymeric structures without negatively impacting the ability of the hydroxyl polymer polymeric structures to be dried (for example to have water removed therefrom).
Accordingly, there is a need for a dual purpose material, for example an ammonium and/or iminium sulfosuccinate diester salt, that performs both a crosslinking facilitator function as well as a fast wetting surfactant function within an aqueous hydroxyl polymer melt composition, which is spun into fibrous elements, such as filaments, while at the same time eliminating the need for additional salts, such as ammonium chloride and/or sodium chloride, being present in the aqueous hydroxyl polymer melt composition and/or fibrous elements produced therefrom as additional crosslinking facilitators.